Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $104.54   13.143%   $118.2797   $118.28   $118.30   $118.30  
  Purchase #2 $184.74   5.818%   $195.4882   $195.49   $195.50   $195.50  
  Purchase #3 $110.32   5.309%   $116.1769   $116.18   $116.20   $116.20  
  Purchase #4 $217.77   4.214%   $226.9468   $226.95   $226.95   $226.90  
  Purchase #5 $104.88   13.758%   $119.3094   $119.31   $119.30   $119.30  
  Purchase #6 $109.60   3.179%   $113.0842   $113.08   $113.10   $113.10  
  Purchase #7 $45.97   6.513%   $48.964   $48.96   $48.95   $49.00  
  7 purchase totals = $877.82       $938.2492   $938.25   $938.30   $938.30